1. Field of the Invention
The present invention relates generally to a printer capable of printing on roll paper and used typically in a point-of-sale (POS) terminal. More specifically, the present invention relates to a printer in which a cover to the roll paper holder in which roll paper is held can be easily opened even when such problems as a roll paper jam occur.
2. Description of the Related Art
Printers for printing to roll paper using an ink jet head, wire dot head, or thermal head for the print head are known in the literature. As taught in JP-A 5-147284, there are also printers capable of printing to both roll paper and slip forms. A printer having a mechanism for switching rotation of a common paper transportation drive motor between a roll paper transportation mechanism and a slip form transportation mechanism is also known from U.S. Pat. No. 5,061,095, for example.
A recording apparatus having a roll paper loading mechanism whereby the cover closing the opening to the roll paper holder of the printer can be fully opened so that replacing or loading roll paper can be accomplished easily is also taught in JP-B 6-79855. It should be noted that the taught recording apparatus has the platen roller (roll paper feed roller), which is pressed against the thermal head, mounted to the edge of the cover to the roll paper holder. The platen roller is also removed from the opening to the roll paper holder when this cover is opened, thus completely exposing the roll paper holder opening. Roll paper can therefore be easily loaded into the holder from a completely unobstructed opening.
When the platen roller is mounted on the cover to the roll paper holder and the cover is then closed, the paper feed gear mounted coaxially to the platen roller engages the last gear (drive gear) in the roll paper transportation gear train on the printer.
In order for these gears to engage, the freely turning paper feed gear first approaches and then contacts the drive gear, and then typically turns a short distance until the teeth on the two gears mesh. Because the platen roller is integrally attached to the paper feed gear, the platen roller also turns slightly as the paper feed gear engages the drive gear. When the cover is opened, the paper feed gear likewise rotates a short distance in the opposite direction to disengage the paper feed gear from the drive gear. The platen roller obviously also turns in the opposite direction at the same time.
JP-A 10-20414 further teaches a cover opening/closing mechanism comprising a cover rotationally attached to the body of a facsimile machine, for example, and an interlock sensor for detecting whether this cover is open or closed. The cover of this cover opening/closing mechanism has a locking means for holding the cover closed to an opposing member. When a release lever for this locking means is operated, the lock is released and the lock and cover separate from the opposing member. The interlock sensor detects that the cover lock has been released.
When the cover is opened to replace the roll paper in a conventional printer having a platen roller and paper feed gear mounted on the cover to the roll paper holder, the paper feed gear for the platen roller mounted to the holder cover rotates slightly so that it is released from engagement with the drive gear train of the printer. It is important to note, however, that the drive gear is always linked to the drive motor through the intervening roll paper transportation gear train. This means that rotation of the drive gear is normally constrained.
In order to open the cover with such a printer, it is therefore necessary to disengage the paper feed gear from the engaged drive gear by working against the motor torque constraining gear movement. Much force is therefore required to open the cover, and the cover cannot be easily opened.
When roll paper jams in such a printer, the paper is typically advanced into and becomes jammed in a gap between the platen roller and another member. When the paper becomes thus jammed, it becomes very difficult if not practically impossible to turn the platen roller and the paper feed gear attached coaxially thereto.
When the user attempts to open the cover in order to remove the jammed roll paper, the paper feed gear will not turn and therefore cannot disengage from the drive gear. It is therefore very difficult if not impossible to open the cover.
Therefore, it is an object of the present invention to overcome the aforementioned problems.
With consideration for the above noted problems, it is an object of the present invention to provide a printer in which the cover to a roll paper holder can be opened using little force.
It is a further object of the present invention to provide a printer in which the cover to a roll paper holder can be opened using little force even when rotation of the roll paper feed roller is constrained due to a roll paper jam.
To achieve these and other objects, a printer according to the present invention comprises: a roll paper holder including an opening for loading the a roll paper, a cover movably supported on the roll paper holder, the cover allowed to move between a closed position where the opening is closed and an opening position where the opening is open, a roll paper feed roller attached to the cover, a motor for rotationally driving the roll paper feed roller, and a roll paper transportation gear train (first gear train) for transferring motor rotation to the roll paper feed roller. This roll paper transportation gear train has a drive gear (first gear) mounted to the roll paper holder, and a paper feed gear (second gear) mounted to the cover for engaging said drive gear when the cover is closed. The printer additionally comprises: a locking mechanism (cover lock) for locking the cover closed; a detector for detecting that the cover lock is unlocked; and a controller for reducing a constraining force exerted to the second gear, which constrains free rotation of the first gear, when the detector detects that the cover lock is unlocked.
When the detector detects that the cover lock is unlocked, the controller preferably drives the motor so as to stop supply of a holding current to said motor.
Alternatively, the controller preferably drives the motor for a specific time in a direction opposite the roll paper advancing direction.
Yet further alternatively, a clutch for disengaging the first gear train from the motor is provided, and the controller disengages the clutch when the detector detects that the cover lock is unlocked.
The clutch in this case preferably comprises a solenoid and a switching gear, and the controller controls solenoid operation. The switching gear can be slid by the solenoid between a roll paper transportation position (first position) where the switching gear engages a gear in the roll paper transportation gear train and a second position at which the switching gear is separated from the roll paper transportation gear train.
When the cover lock in a printer according to the present invention is unlocked, force constraining opening of the cover can thus be reduced or released by stopping the supply of the holding current holding the motor in a particular position, driving the motor in reverse, or disengaging the drive motor from the roll paper transportation gear train.
When the motor holding current is stopped and when the drive motor is disengaged from the roll paper transportation gear train, the drive motor no longer constrains and prevents the roll paper transportation gear train from turning freely. The load on the last drive gear in this gear train is therefore extremely small, enabling the gears to turn freely or with substantially no resistance. As a result, the paper feed gear engaged with this drive gear can also turn extremely easily, and can be disengaged from the drive gear with little force required. As a result, the force required to open the cover is extremely small.
When the motor is driven in reverse, the paper feed gear is forcibly turned for a specific time in the direction in which the cover opens. As a result, the paper feed gear and drive gear are disengaged, and the force required to open the cover is small.
The driving of the of motor in reverse is particularly effective when roll paper becomes jammed and the roll paper feed roller is constrained from turning. Even if the paper feed gear linked to the roll paper feed roller will not turn at this time, the drive gear will. Engagement of the two gears can thus be easily released. The jammed roll paper can also be easily removed by reversing the motor.
In a preferred embodiment of the present invention, the printer further comprises a slip form feed roller; a slip form transportation gear train (second gear train) for transferring motor rotation to the slip form feed roller; and a clutch for selectively engaging the motor to the roll paper transportation gear train or the slip form transportation gear train. The controller in this case drives the clutch to engage the motor to the slip form transportation gear train.
When the cover lock is released in a printer thus comprised, the roll paper transportation gear train is disconnected from the motor. The constraining force of the motor on the roll paper transportation gear train is thus released or reduced, and the last gear in the gear train can turn easily. Little force is therefore required to release the paper feed gear from the drive gear when opening the cover, and the operating force required to open the cover can be reduced.
The clutch can alternatively comprise a solenoid; a switching gear that can be slid by said solenoid between a roll paper transportation position (first position) and a slip form transportation position (second position); a gear in the roll paper transportation gear train for engaging said switching gear in the roll paper transportation position; and a gear in the slip form transportation gear train for engaging said switching gear in the slip form transportation position.
Further preferably, the locking mechanism of this printer according to the present invention comprises a locking lever for locking the cover closed; a pivot pin pivotably supporting said locking lever to pivot between a locked position and an unlocked position; a hook formed as part of the locking lever; and a catch on the roll paper holder for catching the hook when the locking lever reaches the locked position.
Yet further preferably in this case, the detector comprises a pivoting lever, and an optical sensor for detecting the pivoting lever. This pivoting lever is supported in the roll paper holder so that it is positioned in the detection range of the optical sensor when the locking lever is in the locked position, and moves out of this detection range when the locking lever is unlocked.
When thus comprised and the cover will not open because of a roll paper jam, the cover can be easily unlocked by simply operating the locking lever whereby the cover locked closed. The constraining force preventing the paper feed gear from turning can thus be released or reduced without actually moving the cover.
A control method for a printer according to the present invention has steps corresponding to the features of the printer described above, and thus achieves the same results described above.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.